The aim of the study is to determine if an experimental drug, ralfinamide, relieves your neuropathic low back pain, and if it demonstrates superiority to placebo, a "dummy" or sugar pill that contains no active medication. Ralfinamide, given as either 160 mg/day or 320 mg/day, taken in a divided dose twice-a-day, will be compared with placebo. If you are randomly (by chance) selected to receive placebo, you will receive this medication throughout the treatment period of the study. Data from this study will provide essential information for choosing the doses of ralfinamide to be used in the treatment of this type of pain and potentially other types of pain.